The invention was made by an employee of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties.
1. Field of the Invention
This invention relates to optical devices. More specifically, the invention is an optical device capable of achieving a semi-spherical or hemispherical field-of-view.
2. Description of the Related Art
Imaging or illuminating cylindrical, semi-spherical or hemispherical scenes is generally accomplished using a plurality of angular field-of-view cameras/lenses positioned to characterize the necessary field-of-view. Typically, the angular field-of-view of each camera/lens is on the order of 120xc2x0 or less. Thus, multiple cameras/lenses are required to simultaneously view or illuminate, for example, the traffic flow at an intersection, the entire area surrounding a vehicle or structure, or the interior of a room or other structure.
A solution to this problem is a camera/lens having the ability to image or illuminate annularly thereabout, i.e., over an entire 360xc2x0 field-of-view. One such device is a panoramic annular lens (PAL) available commercially from Optechnology Incorporated, Gurley, Ala. The PAL provides a cylindrical or flat annular image about an observation point. A two-dimensional diametrical view of the PAL is shown in FIG. 1 and is referenced generally by 10. Accordingly, the three-dimensional solid structure of a PAL can be visualized by rotating PAL 10 about the Z-axis which passes through the central axis of PAL 10.
The two-dimensional representation of the flat annular image plane of PAL 10 is represented by lines 12 and 14. That is, PAL 10 can be used to image objects on either of lines 12 and 14. For example, the image path for an object on line 12 is indicated by path lines 16A-16D. Path 16A indicates light traveling from line 12 (e.g., the surface of a cylindrical object) to a convex surface 10A of PAL 10. Path 16B indicates refracted light traveling from convex surface 10A through PAL 10 to a convex surface 10B. Convex surface 10B is internally reflective so that path 16C indicates reflected light traveling from the reflective convex surface 10B through PAL 10 to a reflective concave surface 10C. Path 16D indicates reflected light traveling from concave surface 10C through PAL 10 to a flat clear surface 10D, at which point light exits PAL 10. Note that a similar set of path lines could be drawn for an object on line 14 with light entering PAL 10 at convex surface 10E and being reflected at convex surface 10F.
Unfortunately, the three-dimensional realization of a lens based on the two-dimensional diametrical geometry of PAL 10 is difficult to machine with acceptable tolerances. Thus, the PAL based on the two-dimensional geometry described above is limited to use in expensive systems that can tolerate its high-cost of precision manufacturing. Further, the PAL""s forward-looking angular resolution along the Z-axis is limited due to the presence of concave surface 10C.
Accordingly, it is an object of the present invention to provide an optical device capable of being used to image or illuminate a 360xc2x0 field-of-view.
Another object of the present invention is to provide an optical device having a field-of-view that is semi-spherical or hemispherical.
Still another object of the present invention is to provide a 360xc2x0 field-of-view optical device of simple construction.
Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings.
In accordance with the present invention, an optical device has at least a semi-spherical field-of-view. The device comprises a conically-shaped piece of optical material having an annular surface satisfying Snell""s Law for total internal reflection with respect to light passing through the piece and incident on the annular surface from within the piece. The annular surface is symmetric about the device""s longitudinal axis with its exterior being concave.